London - Are you a redhead, but don’t even know it? Research to be released this week indicates millions of Britons carry “silent” genes for redheadedness.

While this does not turn their hair ginger, it may expose them to a range of increased health risks that afflict redheads, such as increased sensitivity to pain, skin cancer, Parkinson’s disease and even Tourette’s syndrome.

In England, six percent of people have red hair; in Scotland, the rate is estimated at 13 percent. Across the rest of Europe the figure is only around four percent.

Now a ground-breaking study of more than 5,000 British people’s DNA indicates that around four in ten of us carry the genes that make hair red - only they are not switched on to influence hair colour: they are “recessive”.

The genes may, however, be at work in other ways that could profoundly affect our health.

The true rate of ginger genes has been revealed by early results from a project called BritainsDNA, which has harnessed scientific expertise from Edinburgh University.

The study examined DNA taken from saliva samples given by 5,000 people from across Britain. Each individual’s genetic signature was determined by analysis performed by experts from the Centre for Population Health Sciences (CPHS) at the University of Edinburgh.

The project is being led by Dr James Wilson, a geneticist who works on the genetic roots of disease.

A senior lecturer at CPHS, Dr Wilson’s research has already uncovered a number of Britain’s hidden DNA secrets, including the fact one in five of us has a gene that means we need almost 30 minutes more sleep each night than usual.

The BritainsDNA other leader, Alistair Moffat, revealed exclusively to the Mail: “Our new results indicate that nearly 40 percent of us carry one of the genes for being red-haired. But the carriers very often have no idea.”

People with Scottish or northern England ancestry are more likely to be “secret” redheads. But the ginger net may be spread much wider than that.

The research project was prompted by Moffat’s own family story. A historian who is also rector of the University of St Andrews, he discovered he carries ginger genes only when his two children unexpectedly turned out red-headed.

The reason for all these redhead genes is down to our cloudy British weather, says Moffat.

While dark skin protects against solar radiation, redheads have evolved pale skin to absorb more of it, important for people in cloudy climes because it helps their bodies produce sufficient vitamin D from the sparse available sunlight to keep healthy.

“That is why most Africans are dark-skinned and most Europeans lighter skinned,” he says. “Light-skinned redheads absorb more vitamin D from sunlight.

“Where there are most redheads, according to statistics, in Scotland and the north of England, there is much more cloud each year thansunshine.”

Red hair appears in people who carry two copies of a gene that changes the way a crucial protein called MC1R behaves.

In people with brown, black and blond hair, the gene produces eumelanin, a pigment that colours hair from blonde to black, depending on how much is present.

But there are three common variants of this gene. These cause the protein to create a different pigment, pheomelanin, and this produces ginger hair and fair skin.

Redheads have any of these threecommon gene variants. In secret redheads, the genes are not ‘expressed’ in a way that affects the colour of theirhair.

The gene mutation can fail to manifest itself over generations, and it does not affect hair colour if a person carries only one copy of the gene.

Investigators have suggested that men with dark hair who grow ginger beards carry a single copy of the recessive gene, but scientific tests have yet to prove this.

There may be no outward signs that you are harbouring this mutation and there may not even be any redheads in your close family. But the mutated redhead genes may be doing other things in your body instead.

“One of the latest links being examined is whether these mutated red-haired genes are linked to an increased risk of babies being born overweight,” says Moffat.

Scientists at University College, London, are using his data because they want to know if hidden redhead genes are playing an important role in increasing babies’ weight, which may have implications for their long-term health.

Other studies have already indicated strong associations between ginger genes and other health issues. The best-known is that redheads are more susceptible to pain.

A 2004 study at the University of Louisville reported that red-haired people require, on average, about 20 percent more general anaesthesia than those with dark or blonde hair. Indeed, fear of excessive pain makes redheads twice as likely to avoid going to the dentist as people with other hair colours, according to a study published in The Journal of the American Dental Association in 2009.

A series of studies involving Dr Daniel Sessler, an anaesthesiologist at the Cleveland Clinic in Ohio, has found that redheads are less responsive than most other people to the commonly used anaesthetics lidocaine and desflurane, and more sensitive to pain caused by hot things such as irons.

Researchers believe that this is down to the same MC1R gene that affects hair colour. They have found MC1R receptors in areas of the brain that are known to influence pain sensation.

It may be that people with hidden redhead genes are also affected in this way, and this could help to explain different people’s pain thresholds.

Most worrying is the link between red hair and skin cancer.

Until very recently it was thought that the reason redheads have the highest risk of the disease is because they burn more easily.

But now it’s been found that the ginger gene can significantly increase their risk of developing melanoma even if they don’t go out in the sun.

A lab study published last month in the highly respected journal Nature looked at red-furred mice with the MC1R gene mutation.

Even without any exposure to sunlight or ultraviolet radiation, the red mice were far more likely to develop melanoma.

On examining the rats’ skin, the scientists found the red-furred rats had less stable cells that were more prone to breaking down and becoming cancerous.

The ginger gene mutations may also explain why redheads appear to have a significantly increased risk of developing Parkinson’s disease. According to researchers at Harvard University who studied more than 140,000 men and women in 2009, redheads have a 90 percent greater than average likelihood of getting Parkinson’s.

Another study published in the journal Proceedings of the National Academy of Sciences suggested that the red-headed hair-colouring pigment pheomelanin may set off a chain of chemical reactions in human brains that can lead to the type of brain-cell damage that causes Parkinson’s.

There is strong statistical evidence for a link between hidden red-hair genes and a significantly increased risk of Tourette’s syndrome, the neurological disorder characterised by repetitive involuntary movements and vocalisations called tics.

A study by Katrina Williams, a professor of developmental medicine at Sydney Children’s Hospital, found that 13 percent of people with Tourette’s in Australia have red hair, while only around four percent of the non-Tourette’s population has this colouring.

Furthermore, more than half of the Tourette’s syndrome patients had relatives with red hair, suggesting a genetic link.

With Tourette’s and Parkinson’s, it is not known whether “silent” redhead genes may also raise the risk of developing problems.

The answers to such questions may soon become clearer, thanks to the launch last week of a Government-backed programme in which up to 100,000 people in England will have their entire genetic make-up mapped.

Meanwhile, Moffat says BritainsDNA has agreed to give its material to experts at University College, London.

“It could prove a great help to health scientists in future,” he says.

“For now, at least, it might help to stop Britons being ‘gingerist’ about redheads. Our studies show that they might very well be secret redheads themselves.” - Daily Mail